A method of manufacturing a plate with an insulating frame by using a metal mold. The plate includes an outer edge portion having a concavo-concave shape, and the metal mold includes a plurality of gate portions for injecting a molding material that forms the frame. The gate portions of the metal mold are at locations that correspond to the concave portions of the metal plate such that when the molding material is injected into the metal mold, an injection pressure of the molding material that can deform the metal plate will not deform the metal plate to an extent that deteriorates insulation resistance that is provided by the frame.